Adjustable delay line



April 19, 1949- J. H. RUBEL ET AL 2,467,857

ADJUSTABLE bELAY LINE Filed Aug. 12, 1945 Inventcrs:

John H. Rubel, Rog BTroell,

Their` Attorneg.

Patented Apr. 19, 1949 U N l TED STATES PTSENT OFFICE ADJUSTABLE DELAY LINE ApplicationAugust `12, 1943, Serial No. 498,380

(Cl. 17d-44) 2 Claims. v1

Our invention relates to 'high frequency signalling systems audit has for its object to provide an improved delay circuit :for use in the transmission of such signals.

In pulse signalling systems of the `type in which a received signal pulse is transmitted to a cathode ray oscilloscope to produce a vertical or radial deflection of the cathode ray beam therein and which employ a sweep -circuit to produce a horizontal or angular kdeflection of the beam, it is desirable to `employ means to delay transmission of the received'pulse tothe proper electrodes of the oscilloscope until operation of the sweep circuit is initiated. Accordingly, it is an object of our invention it-o provide an improved circuit for delaying Ithe transmission of a pulse by a determinable Vperiod of time.

it is another object of our invention to provide a new and improved continuously7 adjustable delaydevice Afor 4a high frequency signalling system.

It is a further object of our invention to provide a new and improved artificial transmission line Vof compact folm and simple construction.

It is -still another object of our invention to provide a new and improved delay circuit for a pulse signalling system in which relatively long delays may .be obtained with vvery little distortion of the pulse signal.

The features Yof our invention Which we believe to be novel are set forth with particularity in the lappended claims. Our invention itself, however, both as to its-organization and method of operation; 4together with further objects and advantages thereof, may best be understood by reference .to :the following Adescription taken in connection `vwith the accompanying drawing, in which Fig. 1 diag-rammatically illustrates an articial transmission line constructed in accordance with our invention and Fig. 2 is an end View of the artiiicial transmission line of Fig. 1. Fig. 3 illustrates diagrammatically a continuously adjustable delay device for a high frequency signalling system. Fig. 4 is a modification of the artiiicial transmission line of Fig. 1 and Fig. 5 is another modification of the artificial transmission line of our invention.

Referring now to Figs. l and 2, jointly, we have shown there an articial transmission line Ill comprising an insulated conductor Il formed into a helical coil of closely Wound turns and surrounding a core of small insulated conductors l 2. A layer of insulation I3 is wrapped around the conductors I2 to form them into a compact core` and the helical coil Il is wound upon this core.l A layer of insulation i4 of any suitable material 2 may be wound about the helically coiled conductor 'l l.

'The conductor li preferably is of solid copper wire covered with a suitable insulating material.

iii, such as a varnish of organic material. The insulated conductors vI2 preferably are formed of lita wire, i. e., a wire composed of iine copper strands, each insulated, and braided together. lThe strands oi the core are soldered together at one end to form an electromagnetic ground which Junctions as the inner conductor of the transmission line lil, the outer conductor being formed by the solenoid or helically coiled conductor il. When constructed in the manner outlined, the line iii has a large distributed capacitance between the electromagnetic ground constituted by the core l2 and the helically coiled conductor El. The transmission line likewise has distributed inductance which consists of the inductanc-e of the coiled conductor l-I. Such an articial transmission line has a relatively low velocity of propagation for currents thereon and functions'toproduce a determinable delay in the transmission of high frequency currents therethrough.

Referring to Fig. 3, we have there shown a device for producing a continuously adjustable delay vin the transmission of high frequency sig` nals. rhis Vdevice comprises a transmission line lll constructed as outlined in the discussion of Fig. l and comprising the helically coiled conductor ii and the core or litz wires l2 soldered together Aat the ends l5 and grounded at these points. This transmission line may be connected Yacross any suitable source of high frequency signals, such as the source i8. The transmission line 'lil formed as a portion of a circle and the source i2 is connected between one terminal oi the coiled conductor ii and ground. The opposite terminal of conductor Il is connected to kground through an impedance 23 whose value is equal to the characteristic impedance Zo ci line lil. Individual turns of the conductor l! are insulated from each other and each turn has an uninsulated portion i9 which is contacted by a movable contact arm 2i). Any suitable output circuit 2l may be connected between the movable contact 2&3 and ground.

In a pulse signalling system, the source I8 may 4confiprise a received signal pulse and the output circuit 2l may comprise the electrodes ci a cathode ray oscilloscope for producing vertical or radial deiiections of the cathode ray beam in the oscilloscope. In such a circuit, by adjustment of the contact arm 2o, a continuously variable delay in the transmission of a received signal pulse from the source i8 to the output circuit may be obtained. Such an arrangement is particularly desirable in signalling systems in which a variable time delay in the transmission of received signals is desired so that the leading edge of the signal appears on the oscilloscope picture when the operation of the sweep circuit has been initiated by the received signal.

1n the modification of our invention shown in Fig. 4, the helically coiled conductor Il woundv about the core of litz wires l2 is surrounded by a braided litz wire 80 which is opened to a desired diameter and slipped over the coiled conductor il or is braided directly over conductor li. In a transmission line constructed as shown in Fig. 4, the distributed capacitance of the line is increased due to the presence of both the core l2 and the braid 80. In this form of our invention, the strands of the braid 30 and the strands of the braid l2 preferably are soldered together at one or both ends to form an electromagnetic ground for the transmission line.

1n Fig. 5, we have shown still another modication of our invention in which the core of litZ wires used in the previously described embodiments is not employed and the insulated conductor l'l is wound as a helical coil of closely wound turns on a substantially cylindrical form 35 of dielectric material and, in turn, is surrounded by a litz wire braid 80. The insulating form preferably is sufliciently rigid to permit accurate winding of the coil Il, yet flexible enough that it can be coiled on a small radius after it has been wound and may be constituted by any suitable dielectric material, for example, molded polyvinylidene chloride. The braided litz wire Si) in this embodiment of the invention is soldered together at one or both ends, or at any desired intermediate point, to function as an electromagnetic ground for the transmission line.

A typical artificial transmission line, constructed as shown in Fig. 5, was formed by a 2.8 mil wire covered with an organic enamel so that its over-all diameter was 3 mils and was wound on a polyvinylidene chloride core having a diameter of fg inch. The solenoid was covered by a single layer of litz braid. Such a delay line, formed of 130 turns of the conductor ll per centimeter of length, was found to have an inductance per centimeter of 30 microhenries and a -capacitance per centimeter of 31 micromicrofarads. This line had a characteristic impedance of 1200 ohms and produced a delay of one micro- Second per 33 centimeters length of the line, the attenuation being only one decibel per microsecond delay. Such a line was found to be particularly suitable for high frequency applications and, when transmitting a one microsecond square wave pulse, produced no significant distortion of the pulse shape.

While we have shown a particular embodiment of our invention, it will of course be understood that we do not wish to be limited thereto since various modifications may be made, and We contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A device for producing a continuously adjustable delay in the transmission of a high frequency signal from a source of signals to an output circuit comprising, a conductor formed into a helical coil of closely wound turns, said turns being insulated from each other, a core of small strands of insulated conductors, said conductors being braided together throughout the length of said core and conductively connected at one end thereof, said source of signals being connected between one end of said coil and said core, said coil having a movable contact, and said output circuit being connected between said movable contact and said core.

2. In a signalling system of the type having a source of high frequency signal and an output circuit, means for delaying the transmission of a signal between the source and the output circuit by an adjustable amount, said means comprising a helical coil of closely wound and insulated turns of a conductor, a core of small insulated wires longitudinally disposed within said coil throughout the length thereof to form therewith a section of transmission line having a low velocity of progagation for signal currents thereon, said wires being braided together throughout the length of said core and being conductively connected at one end thereof, said source being connected between said coil and said core, and means connecting said output circuit to a variable point on said coil.

JOHN H. RUBEL. ROY E. TROELL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,119,245 Cuntz Dec. 1, 1914 1,658,740 Rice Feb. 7, 1928 1,818,027 Affel et al Aug. 11, 1931 1,995,356 Legg Mar. 26, 1935 2,048,450 Horn July 21, 1936 2,387,783 Tawney Oct. 30, 1945 FOREIGN PATENTS Number Country Date 383,528 Great Britain Nov. 17, 1932 

